From the Italian patent application No. 3328 A/85 filed on Feb. 8, 1985 by the present applicants, and corresponding to U.S. application Ser. No. 06/823,582 filed Jan. 26, 1986 (now abandoned) which was replaced by copending application Ser. No. 07/107,885 on Oct. 30, 1987, a dual-use filter sachet for infusion products such as tea, camomile and the like is known. This latter application also discloses a method for producing such dual-use filter sachet continuously, effecting in successive steps all the operations required for the formation of the sachets with the appropriate doses of infusion material, the labelling thereof and the provision of a thread for handling of the filter sachet by the user, starting from the traditional filter-paper strip employed for this purpose.
More particularly, according to the latter application, the dual use filter-paper sachet for infusion products is provided as a multiplicity of successive or serially extending bags or pouches, each of which contains a dosed fraction or unit quantity of the infusion products having a structure conforming to two modes of employment, one being in the form of flat-packed lots for sale wherein said bags or pouches are superimposed on each other or are arranged side by side by folding back a bag or pouch over or adjacent to the other, and one in the unfolded or extended array of said pouches following the action of pressure and traction of the corresponding label covering the handling thread of the filter sachet exerted by the user. The thread has a length which is substantially equal to the length of the sachet in its position of use as unfolded bags or pouches, and is attached to the opposite extremity of said sachet by means of a sticker or tab made of a thermally weldable material, jointly with the label made of non-weldable paper, in the proximity of one of said opposite extremities and is arranged to enfold longitudinally the exterior of the said bags or pouches when the latter are arrayed in their mode of use and packed for sale in lots with folded-back pouches in back-to-back arrangement.
As stated above, Ser. No. 07/107,885 also concerns a method for making such a filter sachet with multiple bags or pouches in succession or in series, starting with a continuously formed flattened tube obtained from strip of thermally weldable filter paper and executing on said tubular strip in succession, while it is being flattened in a continuous movement, the operation of feeding in equidistantly spaced portions of the infusion product; the operations of folding, of longitudinal thermal welding and of sequenced transverse thermal welding to enclose the dosed fractions with each transverse thermal weld so that each of said transverse thermal welds constitutes both the bottom and and the closure seal of the successively contiguous bags or pouches; the feeding-in of the labels arranged at a distance from the transverse median line of the alternate transverse thermal welds and the longitudinal introduction of a continuous thread in contact with the external surface of the preformed flattened tube and that of the stickers or tabs made of thermally weldable material for application through this alternating thermal welds partly to the back of the said labels; the thermal welding of said stickers or tabs so as to connect said thread to said labels and said thread to the said tube by means of the said alternating thermal welds; the sectioning of the said tube thus formed along the said transverse median line of the said alternating transverse thermal welds in portions or pieces comprising at least two successive bags or pouches; the folding back of said portions or pieces conprising at least two bags or pouches about the corresponding intermediary transverse thermal weld so as to superimpose or to set up the pouches side by side; and the joining, by means of thermal welding, of the respectively resulting transverse terminal edges there adjoining with the aid of the corresponding stickers or tabs of thermally weldable material.